Oligothiophene-based nanostructures:: from solution to solid-state aggregates

The possibility to develop optoelectronic devices with improved properties by controlling the degree of organization at the molecular level of organic materials has been driving the design of new pi-conjugated systems. In particular, the organization by self-assembling processes (pi-pi interactions, hydrogen bonding) of well-defined oligomeric systems such as disubstituted oligothiophene derivatives has been demonstrated as a promising approach to conjugated materials with a high degree of structural order of the constituent building blocks. Here, tapping-mode atomic force microscopy is used to investigate the morphologies of (i) thin deposits made from assembly of thiophene-based oligomers starting from molecularly dissolved solutions or (ii) aggregates already formed in solution. In order to understand the results in terms of supramolecular organization, comparisons with molecular modeling simulations are performed. During the self-assembly processes, the interplay between the conjugated molecules, the solvent, and the substrate surface is of primary importance. Depending on the interactions between the molecules and the substrate, one-dimensional (nanowires) or two-dimensional (platelets) objects can be generated. The self-organization of conjugated building blocks in solution or in solid-state on surfaces represents a starting point for the construction of molecular electronics or even circuits, through surface patterning with nanometer-sized objects. (C) 2004 Elsevier B.V. All rights reserved.